Alzie
Afraid all I can suggest is that if you are running XP then use the system restore function.
This should restore your system to an earlier date which might rectify the problem.
Go to Start/All Programs/Accessories/System Tools and then select System Restore. If the problem has only been present for a week or so then restore to a date say a month ago, or even earlier .
If you are running Win 98/ME then you could try updating the drivers for your video card. Just a guess but doing this may help.
Choagy FFCUK The SPL :)